Method and device for applications of selective organ cooling

ABSTRACT

The invention provides a method and device for selectively controlling the temperature of a selected organ of a patient for performance of a specified application. The method includes introducing a guide catheter into a blood vessel. The guide catheter may have a soft tip and a retaining flange, and may be used to provide treatments such as administration of thrombolytic drug therapies, stenting procedures, angiographic procedures, etc. A supply tube is provided having a heat transfer element attached to a distal end thereof. The heat transfer element having a plurality of exterior surface irregularities, these surface irregularities having a depth greater than the boundary layer thickness of flow in the feeding artery of the selected organ. The supply tube and heat transfer element may be inserted through the guide catheter to place the heat transfer element in the feeding artery of the selected organ. Turbulence is created around the surface irregularities at a distance from the heat transfer element greater than the boundary layer thickness of flow in the feeding artery, thereby creating turbulence throughout the blood flow in the feeding artery. A working fluid is circulated into the heat transfer element via the supply tube and via an internal lumen of the heat transfer element. The fluid may be circulated out of the heat transfer element via an external lumen of the heat transfer element and through the guide catheter. Heat is thereby transferred between the heat transfer element and the blood in the feeding artery to selectively control the temperature of the selected organ during or soon before or after the specified application.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional patent application of co-pending U.S. patentapplication Ser. No. 09/215,040 filed on Dec. 16, 1998, U.S. Pat. No.6,251,130 and entitled “Method and Device for Applications of SelectiveOrgan Cooling” which is a continuation-in-part patent application ofco-pending U.S. patent applications: Ser. No. 09/103,342, filed on Jun.23, 1998, U.S. Pat. No. 6,096,068 and entitled “Selective Organ CoolingCatheter and Method of Using the Same”; Ser. No. 09/052,545, filed onMar. 31, 1998, U.S. Pat. No. 6,231,545 and entitled “Circulating FluidHypothermia Method and Apparatus”; Ser. No. 09/047,012, filed on Mar.24, 1998, and entitled “Improved Selective Organ Hypothermia Method andApparatus”, now U.S. Pat. No. 5,957,963 issued on Sep. 28, 1999; Ser.No. 09/215,038, filed on Dec. 16, 1998, U.S. Pat. No. 6,261,312 andentitled “An Inflatable Catheter for Selective Organ Heating and Coolingand Method of Using the Same”; and Ser. No. 09/215,039, filed on Dec.16, 1998, U.S. Pat. No. 6,251,129 and entitled “Method for LowTemperature Thrombolysis and Low Temperature Thrombolytic Agent withSelective Organ Control”; the entirety of each being incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the modification and controlof the temperature of a selected body organ. More particularly, theinvention relates to applications of selective organ cooling whichadvantageously employ complementary techniques.

2. Background Information

Organs in the human body, such as the brain, kidney and heart, aremaintained at a constant temperature of approximately 37° C. Hypothermiacan be clinically defined as a core body temperature of 35° C. or less.Hypothermia is sometimes characterized further according to itsseverity. A body core temperature in the range of 33° C. to 35° C. isdescribed as mild hypothermia. A body temperature of 28° C. to 32° C. isdescribed as moderate hypothermia. A body core temperature in the rangeof 24° C. to 28° C. is described as severe hypothermia.

Hypothermia is uniquely effective in reducing brain injury caused by avariety of neurological insults and may eventually play an importantrole in emergency brain resuscitation. Experimental evidence hasdemonstrated that cerebral cooling improves outcome after globalischemia, focal ischemia, or traumatic brain injury. For this reason,hypothermia may be induced in order to reduce the effect of certainbodily injuries to the brain as well as other organs.

Cerebral hypothermia has traditionally been accomplished through wholebody cooling to create a condition of total body hypothermia in therange of 20° C. to 30° C. However, the use of total body hypothermiarisks certain deleterious systematic vascular effects. For example,total body hypothermia may cause severe derangement of thecardiovascular system, including low cardiac output, elevated systematicresistance, and ventricular fibrillation. Other side effects includerenal failure, disseminated intravascular coagulation, and electrolytedisturbances. In addition to the undesirable side effects, total bodyhypothermia is difficult to administer.

Catheters have been developed which are inserted into the bloodstream ofthe patient in order to induce total body hypothermia. For example, U.S.Pat. No. 3,425,419 to Dato describes a method and apparatus of loweringand raising the temperature of the human body. Dato induces moderatehypothermia in a patient using a metallic catheter. The metalliccatheter has an inner passageway through which a fluid, such as water,can be circulated. The catheter is inserted through the femoral vein andthen through the inferior vena cava as far as the right atrium and thesuperior vena cava. The Dato catheter has an elongated cylindrical shapeand is constructed from stainless steel. By way of example, Datosuggests the use of a catheter approximately 70 cm in length andapproximately 6 mm in diameter. However, use of the Dato deviceimplicates the negative effects of total body hypothermia describedabove.

Due to the problems associated with total body hypothermia, attemptshave been made to provide more selective cooling. For example, coolinghelmets or head gear have been used in an attempt to cool only the headrather than the patient's entire body. However, such methods rely onconductive heat transfer through the skull and into the brain. Onedrawback of using conductive heat transfer is that the process ofreducing the temperature of the brain is prolonged. Also, it isdifficult to precisely control the temperature of the brain when usingconduction due to the temperature gradient that must be establishedexternally in order to sufficiently lower the internal temperature. Inaddition, when using conduction to cool the brain, the face of thepatient is also subjected to severe hypothermia, increasing discomfortand the likelihood of negative side effects. It is known that profoundcooling of the face can cause similar cardiovascular side effects astotal body cooling. From a practical standpoint, such devices arecumbersome and may make continued treatment of the patient difficult orimpossible.

Selected organ hypothermia has been accomplished using extracorporealperfusion, as detailed by Arthur E. Schwartz, M.D. et al., in IsolatedCerebral Hypothermia by Single Carotid Artery Perfusion ofExtracorporeally Cooled Blood in Baboons, which appeared in Vol. 39, No.3, NEUROSURGERY 577 (September, 1996). In this study, blood wascontinually withdrawn from baboons through the femoral artery. The bloodwas cooled by a water bath and then infused through a common carotidartery with its external branches occluded. Using this method, normalheart rhythm, systemic arterial blood pressure and arterial blood gasvalues were maintained during the hypothermia. This study showed thatthe brain could be selectively cooled to temperatures of 20° C. withoutreducing the temperature of the entire body. However, externalcirculation of blood is not a practical approach for treating humansbecause the risk of infection, need for anticoagulation, and risk ofbleeding is too great. Further, this method requires cannulation of twovessels making it more cumbersome to perform particularly in emergencysettings. Even more, percutaneous cannulation of the carotid artery isdifficult and potentially fatal due to the associated arterial walltrauma. Finally, this method would be ineffective to cool other organs,such as the kidneys, because the feeding arteries cannot be directlycannulated percutaneously.

Selective organ hypothermia has also been attempted by perfusion of acold solution such as saline or perflourocarbons. This process iscommonly used to protect the heart during heart surgery and is referredto as cardioplegia. Perfusion of a cold solution has a number ofdrawbacks, including a limited time of administration due to excessivevolume accumulation, cost, and inconvenience of maintaining theperfusate and lack of effectiveness due to the temperature dilution fromthe blood. Temperature dilution by the blood is a particular problem inhigh blood flow organs such as the brain.

BRIEF SUMMARY OF THE INVENTION

The invention provides a practical method and apparatus which modifiesand controls the temperature of a selected organ and which may be usedin combination with many complementary therapeutic techniques.

In one aspect, the invention is directed to a method for selectivelycontrolling the temperature of a selected organ of a patient forperformance of a specified application. The method includes introducinga guide catheter into a blood vessel and providing a supply tube havinga heat transfer element attached to a distal end thereof. The heattransfer element has a plurality of exterior surface irregularities, thesurface irregularities having a depth greater than the boundary layerthickness of flow in the feeding artery of the selected organ. Thesupply tube and heat transfer element are inserted through the guidecatheter to place the heat transfer element in the feeding artery of theselected organ. Turbulence is created around the surface irregularitiesat a distance from the heat transfer element greater than the boundarylayer thickness of flow in the feeding artery, thereby creatingturbulence throughout the blood flow in the feeding artery. A workingfluid is circulated into the heat transfer element via the supply tube.The working fluid is circulated out of the heat transfer element via theguide catheter. Heat is thereby transferred between the heat transferelement and the blood in the feeding artery to selectively control thetemperature of the selected organ.

Implementations of the invention may include one or more of thefollowing. The surface irregularities on the heat transfer element mayinclude a plurality of segments of helical ridges and grooves havingalternating directions of helical rotation. Turbulence may be created byestablishing repetitively alternating directions of helical blood flowwith the alternating helical rotations of the ridges and grooves, andmay be induced for greater than 20% of the period of the cardiac cyclewithin the carotid artery.

In another aspect, the invention relates to a method for selectivethrombolysis by selective vessel hypothermia. The method includesintroducing a guide catheter into a thrombosed blood vessel, deliveringa thrombolytic drug to the blood by flowing the thrombolytic drug intothe guide catheter, and introducing a supply tube having a heat transferelement at a distal end thereof into the thrombosed blood vessel throughthe guide catheter. The heat transfer element is cooled by flowing aworking fluid through the heat transfer element, the return path for theworking fluid being the guide catheter. The blood is thereby cooled to aprespecified temperature by flowing the blood past the heat transferelement. The system may also be used to heat the blood for hyperthermiaapplications.

Implementations of the invention may include one or more of thefollowing. The drug may be chosen from the group consisting of tPA,urokinase, streptokinase, precursors of urokinase, and combinationsthereof. For hypothermia applications, if the thrombolytic drug isstreptokinase, the prespecified temperature range may be between about30° C. and 32° C. If the thrombolytic drug is urokinase or a precursorto urokinase, the prespecified temperature range may be below about 28°C. For hyperthermia applications, if the thrombolytic drug is tPA, theprespecified temperature range may be between about 37° C. to 40° C.

In another aspect, the invention is directed to a selective organ heattransfer device and guide catheter assembly. The assembly includes aguide catheter capable of insertion to a selected feeding artery in thevascular system of a patient, the guide catheter having a soft tip andan interior retaining flange at a distal end. The assembly also includesa flexible supply tube capable of insertion in the guide catheter and aheat transfer element attached to a distal end of the supply tube. Theheat transfer element has a flange at a distal end, the flange capableof engagement with the retaining flange to prevent the heat transferelement from disengaging with the guide catheter. A plurality ofexterior surface irregularities are disposed on the heat transferelement, the surface irregularities being shaped and arranged to createturbulence in surrounding fluid, the surface irregularities having adepth at least equal to the boundary layer thickness of flow in thefeeding artery.

Implementations of the invention include one or more of the following. Astrut may be coupled to the supply tube at a distal end thereof. Theheat transfer element may include a plurality of heat transfer segments,and may further include a flexible joint connecting each of the heattransfer segments to adjacent the heat transfer segments. The flexiblejoint may be a bellows, a metal tube, a plastic tube, a rubber tube, alatex rubber tube, etc.

In another aspect, the invention is directed to a method for performingangiography during selective vessel hypothermia. The method includesintroducing a guide catheter into a blood vessel and delivering aradioopaque fluid to the blood by flowing the radioopaque fluid into theguide catheter. A supply tube having a heat transfer element at a distalend thereof is introduced into the blood vessel through the guidecatheter. The heat transfer element is cooled by flowing a working fluidthrough the heat transfer element, the return path for the working fluidbeing the guide catheter. Blood is thereby cooled by flowing past theheat transfer element. Thus, the cooling can occur at or near the sametime as angiography.

In another aspect, the invention is directed to a method for performingstenting of a stenotic lesion during selective vessel hypothermia. Themethod includes introducing a guide catheter into a blood vessel andintroducing a guide wire through the guide catheter and across astenotic lesion. A balloon catheter loaded with a stent is thendelivered via the guide wire such that the stent is positioned acrossthe lesion. The balloon is expanded with contrast, after which the stentmay be deployed. The heat transfer element and supply tube may then beemployed to cool the blood as described above. Similarly, the coolingcan occur at or near the same time as the stenting procedure.

In another aspect of the invention, a return catheter may be coupled toa heat transfer element, distal end of the heat transfer elementdefining a hole. The return catheter and heat transfer element maytogether form a “guide catheter” through which may be placed a guidewire, a microcatheter, etc. In particular, a catheter may be placedtherein having a tapered shape such that the catheter lodges into thehole. The catheter may have an outlet at a distal end to allow drugdelivery, an outlet upstream of the distal end to allow delivery of aworking fluid to the interior of the heat transfer element, or in somecases both.

Advantages of the invention include the following. The device may beplaced in an artery without traumatizing the arterial wall and withdamaging the device itself. The device may be placed in an artery simplyand by a variety of practitioners such as cardiologists orneurosurgeons. The device allows the complementary performance ofsimultaneous procedures along with brain cooling, these proceduresincluding angiography, stenotic lesion stenting, and drug delivery.

The novel features of this invention, as well as the invention itself,will be best understood from the attached drawings, taken along with thefollowing description, in which similar reference characters refer tosimilar parts, and in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an elevation view of a turbulence inducing heat transferelement within an artery;

FIG. 2 is an elevation view of one embodiment of a heat transfer elementwhich may be employed according to the invention;

FIG. 3 is longitudinal section view of the heat transfer element of FIG.2;

FIG. 4 is a transverse section view of the heat transfer element of FIG.2;

FIG. 5 is a perspective view of the heat transfer element of FIG. 2 inuse within a blood vessel;

FIG. 6 is a cut-away perspective view of an alternative embodiment of aheat transfer element which may be employed according to the invention;

FIG. 7 is a transverse section view of the heat transfer element of FIG.6;

FIG. 8 is a schematic representation of the invention being used in oneembodiment to cool the brain of a patient;

FIG. 9 is a cross-section of a guide catheter which may be employed forapplications of the invention;

FIG. 10 is a schematic representation of the invention being used with areturn tube/guide catheter;

FIG. 11 is a schematic representation of the invention being used with adelivery catheter;

FIG. 12 is a schematic representation of the invention being used with aworking fluid catheter;

FIG. 13 is a schematic representation of the invention being used with aguide wire;

FIG. 14 is a schematic representation of the invention being used with adelivery/working fluid catheter with a balloon attachment; and

FIG. 15 is a second schematic representation of the invention being usedwith a delivery/working fluid catheter with a balloon attachment.

DETAILED DESCRIPTION OF THE INVENTION

The temperature of a selected organ may be intravascularly regulated bya heat transfer element placed in the organ's feeding artery to absorbor deliver heat to or from the blood flowing into the organ. While themethod is described with respect to blood flow into an organ, it isunderstood that heat transfer within a volume of tissue is analogous. Inthe latter case, heat transfer is predominantly by conduction.

The heat transfer may cause either a cooling or a heating of theselected organ. A heat transfer element that selectively alters thetemperature of an organ should be capable of providing the necessaryheat transfer rate to produce the desired cooling or heating effectwithin the organ to achieve a desired temperature.

The heat transfer element should be small and flexible enough to fitwithin the feeding artery while still allowing a sufficient blood flowto reach the organ in order to avoid ischemic organ damage. Feedingarteries, like the carotid artery, branch off the aorta at variouslevels. Subsidiary arteries continue to branch off these initialbranches. For example, the internal carotid artery branches off thecommon carotid artery near the angle of the jaw. The heat transferelement is typically inserted into a peripheral artery, such as thefemoral artery, using a guide catheter or guide wire, and accesses afeeding artery by initially passing though a series of one or more ofthese branches. Thus, the flexibility and size, e.g., the diameter, ofthe heat transfer element are important characteristics. Thisflexibility is achieved as is described in more detail below.

These points are illustrated using brain cooling as an example. Thecommon carotid artery supplies blood to the head and brain. The internalcarotid artery branches off the common carotid artery to supply blood tothe anterior cerebrum. The heat transfer element may be placed into thecommon carotid artery or into both the common carotid artery and theinternal carotid artery.

The benefits of hypothermia described above are achieved when thetemperature of the blood flowing to the brain is reduced to between 30°C. and 32° C. A typical brain has a blood flow rate through each carotidartery (right and left) of approximately 250-375 cubic centimeters perminute (cc/min). With this flow rate, calculations show that the heattransfer element should absorb approximately 75-175 watts of heat whenplaced in one of the carotid arteries to induce the desired coolingeffect. Smaller organs may have less blood flow in their respectivesupply arteries and may require less heat transfer, such as about 25watts.

The method employs conductive and convective heat transfers. Once thematerials for the device and a working fluid are chosen, the conductiveheat transfers are solely dependent on the temperature gradients.Convective heat transfers, by contrast, also rely on the movement offluid to transfer heat. Forced convection results when the heat transfersurface is in contact with a fluid whose motion is induced (or forced)by a pressure gradient, area variation, or other such force. In the caseof arterial flow, the beating heart provides an oscillatory pressuregradient to force the motion of the blood in contact with the heattransfer surface. One of the aspects of the device uses turbulence toenhance this forced convective heat transfer.

The rate of convective heat transfer Q is proportional to the product ofS , the area of the heat transfer element in direct contact with thefluid, ΔT=T_(b)-T_(s), the temperature differential between the surfacetemperature T_(s) of the heat transfer element and the free stream bloodtemperature T_(b), and {overscore (h_(c))}, the average convection heattransfer coefficient over the heat transfer area. {overscore (h_(c))} issometimes called the “surface coefficient of heat transfer” or the“convection heat transfer coefficient”.

The magnitude of the heat transfer rate Q to or from the fluid flow canbe increased through manipulation of the above three parameters.Practical constraints limit the value of these parameters and how muchthey can be manipulated. For example, the internal diameter of thecommon carotid artery ranges from 6 to 8 mm. Thus, the heat transferelement residing therein may not be much larger than 4 mm in diameter toavoid occluding the vessel. The length of the heat transfer elementshould also be limited. For placement within the internal and commoncarotid artery, the length of the heat transfer element is limited toabout 10 cm. This estimate is based on the length of the common carotidartery, which ranges from 8 to 12 cm.

Consequently, the value of the surface area S is limited by the physicalconstraints imposed by the size of the artery into which the device isplaced. Surface features, such as fins, can be used to increase thesurface area of the heat transfer element, however, these features alonecannot provide enough surface area enhancement to meet the required heattransfer rate to effectively cool the brain.

One may also attempt to vary the magnitude of the heat transfer rate byvarying ΔT. The value of ΔT=T_(b)−T_(s) can be varied by varying thesurface temperature T_(s) of the heat transfer element. The allowablesurface temperature of the heat transfer element is limited by thecharacteristics of blood. The blood temperature is fixed at about 37°C., and blood freezes at approximately 0° C. When the blood approachesfreezing, ice emboli may form in the blood which may lodge downstream,causing serious ischemic injury. Furthermore, reducing the temperatureof the blood also increases its viscosity which results in a smalldecrease in the value of {overscore (h_(c))}. Increased viscosity of theblood may further result in an increase in the pressure drop within theartery, thus compromising the flow of blood to the brain. Given theabove constraints, it is advantageous to limit the surface temperatureof the heat transfer element to approximately 1° C.-5° C., thusresulting in a maximum temperature differential between the blood streamand the heat transfer element of approximately 32° C.-36° C.

One may also attempt to vary the magnitude of the heat transfer rate byvarying {overscore (h_(c))}. Fewer constraints are imposed on the valueof the convection heat transfer coefficient {overscore (h_(c))}. Themechanisms by which the value of {overscore (h_(c))} may be increasedare complex. However, one way to increase {overscore (h_(c))} for afixed mean value of the velocity is to increase the level of turbulentkinetic energy in the fluid flow.

The heat transfer rate Q_(no-flow) in the absence of fluid flow isproportional to ΔT, the temperature differential between the surfacetemperature T_(s) of the heat transfer element and the free stream bloodtemperature T_(b) times k, the diffusion constant, and is inverselyproportion to δ, the thickness of the boundary layer.

The magnitude of the enhancement in heat transfer by fluid flow can beestimated by taking the ratio of the heat transfer rate with fluid flowto the heat transfer rate in the absence of fluid flowN=Q_(flow)/Q_(no-flow)={overscore (h_(c))}/(k/δ). This ratio is calledthe Nusselt number (“Nu”). For convective heat transfer between bloodand the surface of the heat transfer element, Nusselt numbers of 30-80have been found to be appropriate for selective cooling applications ofvarious organs in the human body. Nusselt numbers are generallydependent on several other numbers: the Reynolds number, the Womersleynumber, and the Prandtl number.

Stirring-type mechanisms, which abruptly change the direction ofvelocity vectors, may be utilized to induce turbulent kinetic energy andincrease the heat transfer rate. The level of turbulence so created ischaracterized by the turbulence intensity θ. Turbulence intensity θ isdefined as the root mean square of the fluctuating velocity divided bythe mean velocity. Such mechanisms can create high levels of turbulenceintensity in the free stream, thereby increasing the heat transfer rate.This turbulence intensity should ideally be sustained for a significantportion of the cardiac cycle, and should ideally be created throughoutthe free stream and not just in the boundary layer.

Turbulence does occur for a short period in the cardiac cycle anyway. Inparticular, the blood flow is turbulent during a small portion of thedescending systolic flow. This portion is less than 20% of the period ofthe cardiac cycle. If a heat transfer element is placed co-axiallyinside the artery, the heat transfer rate will be enhanced during thisshort interval. For typical of these fluctuations, the turbulenceintensity is at least 0.05. In other words, the instantaneous velocityfluctuations deviate from the mean velocity by at least 5%. Althoughideally turbulence is created throughout the entire period of thecardiac cycle, the benefits of turbulence are obtained if the turbulenceis sustained for 75%, 50% or even as low as 30% or 20% of the cardiaccycle.

One type of turbulence-inducing heat transfer element which may beadvantageously employed to provide heating or cooling of an organ orvolume is described in co-pending U.S. patent application Ser. No.09/103,342 to Dobak and Lasheras for a “Selective Organ Cooling Catheterand Method of Using the Same,” incorporated by reference above. In thatapplication, and as described below, the heat transfer element is madeof a high thermal conductivity material, such as metal. The use of ahighly thermally conductive material increases the heat transfer ratefor a given temperature differential between the coolant within the heattransfer element and the blood. This facilitates the use of a highertemperature coolant within the heat transfer element, allowing safercoolants, such as water, to be used. Highly thermally conductivematerials, such as metals, tend to be rigid. In that application,bellows provided a high degree of articulation that compensated for theintrinsic stiffness of the metal. In an application incorporated byreference above, the bellows are replaced with a straight metal tubehaving a predetermined thickness to allow flexibility via bending of themetal. Alternatively, the bellows may be replaced with a polymer tube,e.g., a latex rubber tube, a plastic tube, or a flexible plasticcorrugated tube.

The device size may be minimized, e.g., less than 4 mm, to preventblockage of the blood flowing in the artery. The design of the heattransfer element should facilitate flexibility in an inherentlyinflexible material.

To create the desired level of turbulence intensity in the blood freestream during the whole cardiac cycle, one embodiment of the device usesa modular design. This design creates helical blood flow and produces ahigh level of turbulence in the free stream by periodically forcingabrupt changes in the direction of the helical blood flow. FIG. 1 is aperspective view of such a turbulence inducing heat transfer elementwithin an artery. Turbulent flow would be found at point 114, in thefree stream area. The abrupt changes in flow direction are achievedthrough the use of a series of two or more heat transfer segments, eachcomprised of one or more helical ridges. To affect the free stream, thedepth of the helical ridge is larger than the thickness of the boundarylayer which would develop if the heat transfer element had a smoothcylindrical surface.

The use of periodic abrupt changes in the helical direction of the bloodflow in order to induce strong free stream turbulence may be illustratedwith reference to a common clothes washing machine. The rotor of awashing machine spins initially in one direction causing laminar flow.When the rotor abruptly reverses direction, significant turbulentkinetic energy is created within the entire wash basin as the changingcurrents cause random turbulent motion within the clothes-water slurry.

FIG. 2 is an elevation view of one embodiment of a heat transfer element14. The heat transfer element 14 is comprised of a series of elongated,articulated segments or modules 20, 22, 24. Three such segments areshown in this embodiment, but two or more such segments could be used.As seen in FIG. 2, a first elongated heat transfer segment 20 is locatedat the proximal end of the heat transfer element 14. Aturbulence-inducing exterior surface of the segment 20 comprises fourparallel helical ridges 28 with four parallel helical grooves 26therebetween. One, two, three, or more parallel helical ridges 28 couldalso be used. In this embodiment, the helical ridges 28 and the helicalgrooves 26 of the heat transfer segment 20 have a left hand twist,referred to herein as a counter-clockwise spiral or helical rotation, asthey proceed toward the distal end of the heat transfer segment 20.

The first heat transfer segment 20 is coupled to a second elongated heattransfer segment 22 by a first tube section 25, which providesflexibility. The second heat transfer segment 22 comprises one or morehelical ridges 32 with one or more helical grooves 30 therebetween. Theridges 32 and grooves 30 have a right hand, or clockwise, twist as theyproceed toward the distal end of the heat transfer segment 22. Thesecond heat transfer segment 22 is coupled to a third elongated heattransfer segment 24 by a second tube section 27. The third heat transfersegment 24 comprises one or more helical ridges 36 with one or morehelical grooves 34 therebetween. The helical ridge 36 and the helicalgroove 34 have a left hand, or counter-clockwise, twist as they proceedtoward the distal end of the heat transfer segment 24. Thus, successiveheat transfer segments 20, 22, 24 of the heat transfer element 14alternate between having clockwise and counterclockwise helical twists.The actual left or right hand twist of any particular segment isimmaterial, as long as adjacent segments have opposite helical twist.

In addition, the rounded contours of the ridges 28, 32, 36 also allowthe heat transfer element 14 to maintain a relatively atraumaticprofile, thereby minimizing the possibility of damage to the bloodvessel wall. A heat transfer element may be comprised of two, three, ormore heat transfer segments.

The tube sections 25, 27 are formed from seamless and nonporousmaterials, such as metal, and therefore are impermeable to gas, whichcan be particularly important, depending on the type of working fluidwhich is cycled through the heat transfer element 14. The structure ofthe tube sections 25, 27 allows them to bend, extend and compress, whichincreases the flexibility of the heat transfer element 14 so that it ismore readily able to navigate through blood vessels. The tube sections25, 27 are also able to tolerate cryogenic temperatures without a lossof performance. The tube sections 25, 27 may have a predeterminedthickness of their walls, such as between about 0.5 and 0.8 mils. Thepredetermined thickness is to a certain extent dependent on the diameterof the overall tube. Thicknesses of 0.5 to 0.8 mils may be appropriateespecially for a tubal diameter of about 4 mm. For smaller diameters,such as about 3.3 mm, larger thicknesses may be employed for higherstrength. In another embodiment, tube sections 25, 27 may be formed froma polymer material such as rubber, e.g., latex rubber.

The exterior surfaces of the heat transfer element 14 can be made frommetal except in flexible joint embodiment where the surface may becomprised of a polymer material. The metal may be a very high thermalconductivity material such as nickel, thereby facilitating efficientheat transfer. Alternatively, other metals such as stainless steel,titanium, aluminum, silver, copper and the like, can be used, with orwithout an appropriate coating or treatment to enhance biocompatibilityor inhibit clot formation. Suitable biocompatible coatings include,e.g., gold, platinum or polymer paralyene. The heat transfer element 14may be manufactured by plating a thin layer of metal on a mandrel thathas the appropriate pattern. In this way, the heat transfer element 14may be manufactured inexpensively in large quantities, which is animportant feature in a disposable medical device.

Because the heat transfer element 14 may dwell within the blood vesselfor extended periods of time, such as 24-48 hours or even longer, it maybe desirable to treat the surfaces of the heat transfer element 14 toavoid clot formation. One means by which to prevent thrombus formationis to bind an antithrombogenic agent to the surface of the heat transferelement 14. For example, heparin is known to inhibit clot formation andis also known to be useful as a biocoating. Alternatively, the surfacesof the heat transfer element 14 may be bombarded with ions such asnitrogen. Bombardment with nitrogen can harden and smooth the surfaceand, thus prevent adherence of clotting factors to the surface.

FIG. 3 is a longitudinal sectional view of the heat transfer element 14,taken along line 3—3 in FIG. 2. Some interior contours are omitted forpurposes of clarity. An inner tube 42 creates an inner coaxial lumen 42and an outer coaxial lumen 46 within the heat transfer element 14. Oncethe heat transfer element 14 is in place in the blood vessel, a workingfluid such as saline or other aqueous solution may be circulated throughthe heat transfer element 14. Fluid flows up a supply catheter into theinner coaxial lumen 40. At the distal end of the heat transfer element14, the working fluid exits the inner coaxial lumen 40 and enters theouter lumen 46. As the working fluid flows through the outer lumen 46,heat is transferred from the working fluid to the exterior surface 37 ofthe heat transfer element 14. Because the heat transfer element 14 isconstructed from a high conductivity material, the temperature of itsexterior surface 37 may reach very close to the temperature of theworking fluid. The tube 42 may be formed as an insulating divider tothermally separate the inner lumen 40 from the outer lumen 46. Forexample, insulation may be achieved by creating longitudinal airchannels in the wall of the insulating tube 42. Alternatively, theinsulating tube 42 may be constructed of a non-thermally conductivematerial like polytetrafluoroethylene or some other polymer.

It is important to note that the same mechanisms that govern the heattransfer rate between the exterior surface 37 of the heat transferelement 14 and the blood also govern the heat transfer rate between theworking fluid and the interior surface 38 of the heat transfer element14. The heat transfer characteristics of the interior surface 38 areparticularly important when using water, saline or other fluid whichremains a liquid as the coolant. Other coolants such as freon undergonucleate boiling and create turbulence through a different mechanism.Saline is a safe coolant because it is non-toxic, and leakage of salinedoes not result in a gas embolism, which could occur with the use ofboiling refrigerants. Since turbulence in the coolant is enhanced by theshape of the interior surface 38 of the heat transfer element 14, thecoolant can be delivered to the heat transfer element 14 at a warmertemperature and still achieve the necessary heat transfer rate.

This has a number of beneficial implications in the need for insulationalong the catheter shaft length. Due to the decreased need forinsulation, the catheter shaft diameter can be made smaller. Theenhanced heat transfer characteristics of the interior surface of theheat transfer element 14 also allow the working fluid to be delivered tothe heat transfer element 14 at lower flow rates and lower pressures.High pressures may make the heat transfer element stiff and cause it topush against the wall of the blood vessel, thereby shielding part of theexterior surface 37 of the heat transfer element 14 from the blood.Because of the increased heat transfer characteristics achieved by thealternating helical ridges 28, 32, 36, the pressure of the working fluidmay be as low as 5 atmospheres, 3 atmospheres, 2 atmospheres or evenless than 1 atmosphere.

FIG. 4 is a transverse sectional view of the heat transfer element 14,taken at a location denoted by the line 4—4 in FIG. 2. FIG. 4illustrates a five-lobed embodiment, whereas FIG. 2 illustrates afour-lobed embodiment. As mentioned earlier, any number of lobes mightbe used. In FIG. 4, the coaxial construction of the heat transferelement 14 is clearly shown. The inner coaxial lumen 40 is defined bythe insulating coaxial tube 42. The outer lumen 46 is defined by theexterior surface of the insulating coaxial tube 42 and the interiorsurface 38 of the heat transfer element 14. In addition, the helicalridges 32 and helical grooves 30 may be seen in FIG. 4. As noted above,in the preferred embodiment, the depth of the grooves, d_(i), is greaterthan the boundary layer thickness which would have developed if acylindrical heat transfer element were introduced. For example, in aheat transfer element 14 with a 4 mm outer diameter, the depth of theinvaginations, d_(i), may be approximately equal to 1 mm if designed foruse in the carotid artery. Although FIG. 4 shows four ridges and fourgrooves, the number of ridges and grooves may vary. Thus, heat transferelements with 1, 2, 3, 4, 5, 6, 7, 8 or more ridges are specificallycontemplated.

FIG. 5 is a perspective view of a heat transfer element 14 in use withina blood vessel, showing only one helical lobe per segment for purposesof clarity. Beginning from the proximal end of the heat transfer element(not shown in FIG. 5), as the blood moves forward during the systolicpulse, the first helical heat transfer segment 20 induces acounter-clockwise rotational inertia to the blood. As the blood reachesthe second segment 22, the rotational direction of the inertia isreversed, causing turbulence within the blood. Further, as the bloodreaches the third segment 24, the rotational direction of the inertia isagain reversed. The sudden changes in flow direction actively reorientand randomize the velocity vectors, thus ensuring turbulence throughoutthe bloodstream. During turbulent flow, the velocity vectors of theblood become more random and, in some cases, become perpendicular to theaxis of the artery. In addition, as the velocity of the blood within theartery decreases and reverses direction during the cardiac cycle,additional turbulence is induced and turbulent motion is sustainedthroughout the duration of each pulse through the same mechanismsdescribed above.

Thus, a large portion of the volume of warm blood in the vessel isactively brought in contact with the heat transfer element 14, where itcan be cooled by direct contact rather than being cooled largely byconduction through adjacent laminar layers of blood. As noted above, thedepth of the grooves 26, 30, 34 (FIG. 2) is greater than the depth ofthe boundary layer which would develop if a straight-walled heattransfer element were introduced into the blood stream. In this way,free stream turbulence is induced. In the preferred embodiment, in orderto create the desired level of turbulence in the entire blood streamduring the whole cardiac cycle, the heat transfer element 14 creates aturbulence intensity greater than about 0.05. The turbulence intensitymay be greater than 0.05, 0.06, 0.07 or up to 0.10 or 0.20 or greater.

Referring back to FIG. 2, the heat transfer element 14 has been designedto address all of the design criteria discussed above. First, the heattransfer element 14 is flexible and is made of a highly conductivematerial. The flexibility is provided by a segmental distribution oftube sections 25, 27 which provide an articulating mechanism. The tubesections have a predetermined thickness which provides sufficientflexibility. Second, the exterior surface area 37 has been increasedthrough the use of helical ridges 28, 32, 36 and helical grooves 26, 30,34. The ridges also allow the heat transfer element 14 to maintain arelatively atraumatic profile, thereby minimizing the possibility ofdamage to the vessel wall. Third, the heat transfer element 14 has beendesigned to promote turbulent kinetic energy both internally andexternally. The modular or segmental design allows the direction of theinvaginations to be reversed between segments. The alternating helicalrotations create an alternating flow that results in mixing the blood ina manner analogous to the mixing action created by the rotor of awashing machine that switches directions back and forth. This mixingaction is intended to promote high level turbulent kinetic energy toenhance the heat transfer rate. The alternating helical design alsocauses beneficial mixing, or turbulent kinetic energy, of the workingfluid flowing internally.

FIG. 6 is a cut-away perspective view of an alternative embodiment of aheat transfer element 50. An external surface 52 of the heat transferelement 50 is covered with a series of axially staggered protrusions 54.The staggered nature of the outer protrusions 54 is readily seen withreference to FIG. 7 which is a transverse cross-sectional view taken ata location denoted by the line 7—7 in FIG. 6. In order to induce freestream turbulence, the height, d_(p), of the staggered outer protrusions54 is greater than the thickness of the boundary layer which woulddevelop if a smooth heat transfer element had been introduced into theblood stream. As the blood flows along the external surface 52, itcollides with one of the staggered protrusions 54 and a turbulent wakeflow is created behind the protrusion. As the blood divides and swirlsalong side of the first staggered protrusion 54, its turbulent wakeencounters another staggered protrusion 54 within its path preventingthe re-lamination of the flow and creating yet more turbulence. In thisway, the velocity vectors are randomized and turbulence is created notonly in the boundary layer but throughout the free stream. As is thecase with the preferred embodiment, this geometry also induces aturbulent effect on the internal coolant flow.

A working fluid is circulated up through an inner coaxial lumen 56defined by an insulating coaxial tube 58 to a distal tip of the heattransfer element 50. The working fluid then traverses an outer coaxiallumen 60 in order to transfer heat to the exterior surface 52 of theheat transfer element 50. The inside surface of the heat transferelement 50 is similar to the exterior surface 52, in order to induceturbulent flow of the working fluid. The inner protrusions can bealigned with the outer protrusions 54, as shown in FIG. 7, or they canbe offset from the outer protrusions 54, as shown in FIG. 6.

FIG. 8 is a schematic representation of the invention being used to coolthe brain of a patient. The selective organ hypothermia apparatus shownin FIG. 8 includes a working fluid supply 10, preferably supplying achilled liquid such as water, alcohol or a halogenated hydrocarbon, asupply catheter 12 and the heat transfer element 14. The supply catheter12 has a coaxial construction. An inner coaxial lumen within the supplycatheter 12 receives coolant from the working fluid supply 10. Thecoolant travels the length of the supply catheter 12 to the heattransfer element 14 which serves as the cooling tip of the catheter. Atthe distal end of the heat transfer element 14, the coolant exits theinsulated interior lumen and traverses the length of the heat transferelement 14 in order to decrease the temperature of the heat transferelement 14. The coolant then traverses an outer lumen of the supplycatheter 12 so that it may be disposed of or recirculated. The supplycatheter 12 is a flexible catheter having a diameter sufficiently smallto allow its distal end to be inserted percutaneously into an accessibleartery such as the femoral artery of a patient as shown in FIG. 8. Thesupply catheter 12 is sufficiently long to allow the heat transferelement 14 at the distal end of the supply catheter 12 to be passedthrough the vascular system of the patient and placed in the internalcarotid artery or other small artery. The method of inserting thecatheter into the patient and routing the heat transfer element 14 intoa selected artery is well known in the art.

Although the working fluid supply 10 is shown as an exemplary coolingdevice, other devices and working fluids may be used. For example, inorder to provide cooling, freon, perflourocarbon, water, or saline maybe used, as well as other such coolants.

The heat transfer element can absorb or provide over 75 Watts of heat tothe blood stream and may absorb or provide as much as 100 Watts, 150Watts, 170 Watts or more. For example, a heat transfer element with adiameter of 4 mm and a length of approximately 10 cm using ordinarysaline solution chilled so that the surface temperature of the heattransfer element is approximately 5° C. and pressurized at 2 atmospherescan absorb about 100 Watts of energy from the bloodstream. Smallergeometry heat transfer elements may be developed for use with smallerorgans which provide 60 Watts, 50 Watts, 25 Watts or less of heattransfer.

The practice of the present invention is illustrated in the followingnon-limiting example.

EXEMPLARY PROCEDURE

1. The patient is initially assessed, resuscitated, and stabilized.

2. The procedure is carried out in an angiography suite or surgicalsuite equipped with fluoroscopy.

3. Because the catheter is placed into the common carotid artery, it isimportant to determine the presence of stenotic atheromatous lesions. Acarotid duplex (Doppler/ultrasound) scan can quickly and non-invasivelymake this determination. The ideal location for placement of thecatheter is in the left carotid so this may be scanned first. If diseaseis present, then the right carotid artery can be assessed. This test canbe used to detect the presence of proximal common carotid lesions byobserving the slope of the systolic upstroke and the shape of thepulsation. Although these lesions are rare, they could inhibit theplacement of the catheter. Examination of the peak blood flow velocitiesin the internal carotid can determine the presence of internal carotidartery lesions. Although the catheter is placed proximally to suchlesions, the catheter may exacerbate the compromised blood flow createdby these lesions. Peak systolic velocities greater that 130 cm/sec andpeak diastolic velocities>100 cm/sec in the internal indicate thepresence of at least 70% stenosis. Stenosis of 70% or more may warrantthe placement of a stent to open up the internal artery diameter.

4. The ultrasound can also be used to determine the vessel diameter andthe blood flow and the catheter with the appropriately sized heattransfer element could be selected.

5. After assessment of the arteries, the patients inguinal region issterilely prepped and infiltrated with lidocaine.

6. The femoral artery is cannulated and a guide wire may be inserted tothe desired carotid artery. Placement of the guide wire is confirmedwith fluoroscopy.

7. An angiographic catheter can be fed over the wire and contrast mediainjected into the artery to further to assess the anatomy of thecarotid.

8. Alternatively, the femoral artery is cannulated and a 10-12.5 french(f) introducer sheath is placed.

9. A guide catheter is placed into the desired common carotid artery. Ifa guiding catheter is placed, it can be used to deliver contrast mediadirectly to further assess carotid anatomy.

10. A 10f-12 f (3.3-4.0 mm) (approximate) cooling catheter issubsequently filled with saline and all air bubbles are removed.

11. The cooling catheter is placed into the carotid artery via theguiding catheter or over the guidewire. Placement is confirmed withfluoroscopy.

12. Alternatively, the cooling catheter tip is shaped (angled or curvedapproximately 45 degrees), and the cooling catheter shaft has sufficientpushability and torqueability to be placed in the carotid without theaid of a guide wire or guide catheter.

13. The cooling catheter is connected to a pump circuit also filled withsaline and free from air bubbles. The pump circuit has a heat exchangesection that is immersed into a water bath and tubing that is connectedto a peristaltic pump. The water bath is chilled to approximately 0° C.

14. Cooling is initiated by starting the pump mechanism. The salinewithin the cooling catheter is circulated at 5 cc/sec. The salinetravels through the heat exchanger in the chilled water bath and iscooled to approximately 1° C.

15. It subsequently enters the cooling catheter where it is delivered tothe heat transfer element. The saline is warmed to approximately 5-7° C.as it travels along the inner lumen of the catheter shaft to the end ofthe heat transfer element.

16. The saline then flows back through the heat transfer element incontact with the inner metallic surface. The saline is further warmed inthe heat transfer element to 12 -15° C., and in the process, heat isabsorbed from the blood, cooling the blood to 30° C. to 32° C.

17. The chilled blood then goes on to chill the brain. It is estimatedthat 15-30 minutes will be required to cool the brain to 30 to 32° C.

18. The warmed saline travels back down the outer lumen of the cathetershaft and back to the chilled water bath where it is cooled to 1° C.

19. The pressure drops along the length of the circuit are estimated tobe 2-3 atmospheres.

20. The cooling can be adjusted by increasing or decreasing the flowrate of the saline. Monitoring of the temperature drop of the salinealong the heat transfer element will allow the flow to be adjusted tomaintain the desired cooling effect.

21. The catheter is left in place to provide cooling for 12 to 24 hours.

22. If desired, warm saline can be circulated to promote warming of thebrain at the end of the procedure.

The invention may also be used in combination with other techniques. Forexample, one technique employed to place working lumens or catheters indesired locations employs guide catheters, as mentioned above. Referringto FIG. 9, a guide catheter 102 is shown which may be advantageouslyemployed in the invention. The guide catheter 102 has a soft tapered tip104 and a retaining flange 124 at a distal end 101. The soft tapered tip104 allows an atraumatic entrance of the guide catheter 102 into anartery as well as a sealing function as is described in more detailbelow. The retaining flange 124 may be a metallic member adhered to theguide catheter interior wall or may be integral with the material of thetube. The retaining flange 124 further has a sealing function describedin more detail below.

The guide catheter 102 may have various shapes to facilitate placementinto particular arteries. In the case of the carotid artery, the guidecatheter 102 may have the shape of a hockey stick. The guide catheter102 may include a Pebax® tube with a Teflon® liner. The Teflon® linerprovides sufficient lubricity to allow minimum friction when componentsare pushed through the tube. A metal wire braid may also be employedbetween the Pebax® tube and the Teflon® liner to provide torqueabilityof the guide catheter 102.

A number of procedures may be performed with the guide catheter 102 inplace within an artery. For example, a stent may be disposed across astenotic lesion in the internal carotid artery. This procedure involvesplacing a guide wire through the guide catheter 102 and across thelesion. A balloon catheter loaded with a stent is then advanced alongthe guide wire. The stent is positioned across the lesion. The balloonis expanded with contrast, and the stent is deployed intravascularly toopen up the stenotic lesion. The balloon catheter and the guide wire maythen be removed from the guide catheter.

A variety of treatments may pass through the guide catheter. Forexample, the guide catheter, or an appropriate lumen disposed within,may be employed to transfer contrast for diagnosis of bleeding orarterial blockage, such as for angiography. The same may further beemployed to deliver various drug therapies, e.g., to the brain. Suchtherapies may include delivery of thrombolytic drugs that lyse clotslodged in the arteries of the brain, as are further described in anapplication incorporated by reference above.

A proximal end 103 of the guide catheter 102 has a male luer connectorfor mating with a y-connector 118 attached to a supply tube 108. Thesupply tube 108 may include a braided Pebax® tube or a polyimide tube.The y-connector 118 connects to the guide catheter 102 via a male/femaleluer connector assembly 116. The y-connector 118 allows the supply tube108 to enter the assembly and to pass through the male/female luerconnector assembly 116 into the interior of the guide catheter 102. Thesupply tube 108 may be disposed with an outlet at its distal end. Theoutlet of the supply tube 108 may also be used to provide a workingfluid to the interior of a heat transfer element 110. The guide catheter102 may be employed as the return tube for the working fluid supply inthis aspect of the invention. In this embodiment, a heat transferelement 110 is delivered to the distal end 101 of the guide catheter 102as is shown in FIG. 10.

In FIG. 10, the heat transfer element 110 is shown, nearly in a workinglocation, in combination with the return tube/guide catheter 102. Inparticular, the heat transfer element 110 is shown near the distal end101 of the return tube/guide catheter (“RTGC”) 102. The heat transferelement 110 may be kept in place by a flange 106 on the heat transferelement 110 that abuts the retaining flange 124 on the RTGC 102. Flanges124 and 106 may also employ o-rings such as an o-ring 107 shown adjacentto the flange 106. Other such sealing mechanisms or designs may also beused. In this way, the working fluid is prevented from leaking into theblood.

The supply tube 108 may connect to the heat transfer element 110 (theconnection is not shown) and may be employed to push the heat transferelement 110 through the guide catheter 102. The supply tube should havesufficient rigidity to accomplish this function. In an alternativeembodiment, a guide wire may be employed having sufficient rigidity topush both the supply tube 108 and the heat transfer element 110 throughthe guide catheter 102. So that the supply tube 108 is preventing fromabutting its outlet against the interior of the heat transfer element110 and thereby stopping the flow of working fluid, a strut 112 may beemployed on a distal end of the supply tube 108. The strut 112 may havea window providing an alternative path for the flowing working fluid.

The heat transfer element 110 may employ any of the forms disclosedabove, as well as variations of those forms. For example, the heattransfer element 110 may employ alternating helical ridges separated byflexible joints, the ridges creating sufficient turbulence to enhanceheat transfer between a working fluid and blood in the artery.Alternatively, the heat transfer element 110 may be inflatable and mayhave sufficient surface area that the heat transfer due to conductionalone is sufficient to provide the requisite heat transfer. Details ofthe heat transfer element 110 are omitted in FIG. 10 for clarity.

FIG. 11 shows an alternate embodiment of the invention in which a heattransfer element 204 employs an internal supply catheter 216. The heattransfer element 204 is shown with turbulence-inducing invaginations 218located thereon. Similar invaginations may be located in the interior ofthe heat transfer element 204 but are not shown for clarity. Further, itshould be noted that the heat transfer element 204 is shown with merelyfour invaginations. Other embodiments may employ multiple elementsconnected by flexible joints as is disclosed above. The single heattransfer element shown in FIG. 11 is provided merely for clarity.

A return supply catheter 202 is shown coupled to the heat transferelement 204. The return supply catheter may be coupled to the heattransfer element 204 in known fashion, and may provide a convenientreturn path for working fluid as may be provided to the heat transferelement 204 to provide temperature control of a flow or volume of blood.

A delivery catheter 216 is also shown in FIG. 11. The delivery catheter216 may be coupled to a y-connector at its proximal end in the mannerdisclosed above. The delivery catheter 216 may be freely disposed withinthe interior of the return supply catheter 202 except where it isrestrained from further longitudinal movement (in one direction) by aretaining flange 210 disposed at the distal end 208 of the heat transferelement 204. The delivery catheter 216 may be made sufficiently flexibleto secure itself within retaining flange 210, at least for a shortduration. The delivery catheter 216 may have a delivery outlet 212 at adistal end to allow delivery of a drug or other such material fortherapeutic purposes. For example, a radioopaque fluid may be dispensedfor angiography or a thrombolytic drug for thrombinolysis applications.

For applications in which it is desired to provide drainage of theartery, e.g., laser ablation, the delivery catheter may be pulledupstream of the retaining flange 210, exposing an annular hole in fluidcommunication with the return supply catheter 202. The return supplycatheter 202 may then be used to drain the volume adjacent the retainingflange 210.

The assembly may also perform temperature control of blood in the arterywhere the same is located. Such temperature control procedures may beperformed, e.g., before or after procedures involving the deliverycatheter 216. Such a device for temperature control is shown in FIG. 12.In this figure, a working fluid catheter 222 is disposed within thereturn supply catheter 202 and the heat transfer element 204. In amanner similar to the delivery catheter 216, the working fluid cathetermay be freely disposed within the interior of the return supply catheter202 and may further be coupled to a y-connector at its proximal end inthe manner disclosed above. The working fluid catheter 222 may furtherbe made sufficiently flexible to secure itself within retaining flange210, at least for a short duration. The working fluid catheter 222 mayhave a plurality of outlets 214 to allow delivery of a working fluid.The outlets 214 are located near the distal end 224 of the working fluidcatheter 222 but somewhat upstream. In this way, the outlets 214 allowdispensation of a working fluid into the interior of the heat transferelement 204 rather than into the blood stream. The working fluidcatheter 222 may also be insulated to allow the working fluid tomaintain a desired temperature without undue heat losses to the walls ofthe working fluid catheter 222.

One way of using the same catheter as a delivery catheter and as aworking fluid catheter is shown in FIGS. 14 and 15. In FIG. 14, adelivery/working fluid catheter 248 is shown in a position similar tothe respective catheters of FIGS. 11 and 12. The delivery/working fluidcatheter 248 has working fluid outlets and a delivery outlet, and isfurther equipped with a balloon 244 disposed at the distal end. Balloon244 may be inflated with a separate lumen (not shown). By retracting thedelivery/working fluid catheter 248 to the position shown in FIG. 15,the balloon 244 may be made to seal the hole defined by retaining flange210, thereby creating a fluid-tight seal so that working fluid may bedispensed from outlets 246 to heat or cool the heat transfer element204.

One method of disposing a heat transfer device within a desired artery,such as the carotid artery, involves use of a guide wire. Referring toFIG. 13, a guide wire 232 is shown disposed within the interior of theheat transfer element 204. The heat transfer element 204 mayconveniently use the hole defined by retaining flange 210 to be threadedonto the guide wire 232.

Numerous other therapies may then employ the return supply catheter andheat transfer element as a “guide catheter”. For example, various laserand ultrasound ablation catheters may be disposed within. In this way,these therapeutic techniques may be employed at nearly the same time astherapeutic temperature control, including, e.g., neuroprotectivecooling.

The invention has also been described with respect to certainembodiments. It will be clear to one of skill in the art that variationsof the embodiments may be employed in the method of the invention.Accordingly, the invention is limited only by the scope of the appendedclaims.

What is claimed is:
 1. A method for performing stenting of a stenoticlesion during selective vessel hypothermia, comprising: introducing aguide catheter into a blood vessel; introducing a guide wire through theguide catheter and across a stenotic lesion; delivering a ballooncatheter loaded with a stent via the guide wire; positioning the stentacross the lesion; expanding the balloon; deploying the stent;introducing a supply tube having a transfer element at a distal endthereof into the blood vessel through the guide catheter; and coolingthe heat transfer element, by flowing a working fluid through the heattransfer element, wherein the heat transfer element is not used todeploy the stent, and further wherein blood in the blood vessel iscooled to a prespecified temperature range by flowing past the heattransfer element.
 2. The method of claim 1, wherein the heat element hasa plurality of exterior surface irregularities, the surfaceirregularities having a depth greater than the boundary layer thicknessof flow in the blood vessel.
 3. The method of claim 2, furthercomprising the step of: creating turbulence around the surfaceirregularities at a distance from the heat transfer element greater thanthe boundary layer thickness of flow in the blood vessel, therebycreating turbulence throughout the blood flow in the blood vessel. 4.The method of claim 3, wherein: the surface irregularities on the heattransfer element comprise a plurality of segments of helical ridges andgrooves having alternating directions of helical rotation; andturbulence is created by establishing repetitively alternatingdirections of helical blood flow with the alternating helical rotationsof the ridges and grooves.
 5. The method of claim 1, wherein the step ofintroducing a supply tube having a heat transfer element occurs at ornear the same time as the step of deploying the stent.
 6. The method ofclaim 1, wherein the step of introducing a supply tube having a heattransfer element occurs after the step of deploying the stent.